Abstract:
Northeastern Himalayan hill region of India is known to produce quality mandarin (C.
reticulata) commercially. Citrus tristeza virus (CTV), an aphid (Toxoptera citricidus)
transmitted closterovirus, is a major problem to cause decline of mandarin in this region.
The different orchards of Mirik in the Darjeeling and Rumtek of East Sikkim were
surveyed. CTV incidence of 48-53.3% in Mirik and 40-60% in Rumtek were estimated
using direct antigen coated-ELISA and polymerase chain reaction. Nine CTV isolates; 6
from Mirik and 3 from Rumtek were characterized based on sequencing of 5’ORF1a gene
fragments (404nt) and CP gene (672nt). The present isolates shared 85-100% nt identity
and formed 3 genogroups for 5’ ORF1a; and 91-100% nt identity and formed 4
genogroups for CP gene, among them. Majorities of the present isolates are related with
decline inducing Indian isolate Kpg3 indicating decline inducing CTV isolates are
common in this region. CTV isolates of Sikkim were characterized for the first time and all
the Sikkim isolates are genetically related with CTV isolate Kpg3. One new CTV isolate
K38 related to the severe Florida isolate T3 was reported from Mirik. The recombination detecting program RDP4 identified two CTV isolates K37 and K38 of Mirik as putative
recombinants. The previous and the present studies report occurrence of at least five CTV
variants in Northeastern Himalayan hill region of India.
